As is well recognized in the industry, there has long been a need to develop and to provide a fuel burning system which is capable of burning a liquid fuel in a very efficient manner and without the side effects of inadequate combustion which lead to the omission of pollutants into the atmosphere.
In the case of residential oil burners, the burner must operate with low smoke emissions to prevent sooting of the heat exchanger and objectionably high smoke levels in residential neighborhoods. The result is that large amounts of excess air must be introduced in the residential combustion process to assure that the burner operates at acceptable smoke levels.
It is well known that conventional oil burners burn very differently when they are placed in different type furnaces. This is because of the poor fuel atomization of current high pressure oil burners, which when installed in a furnace, cause some of the oil particles that discharge from the nozzle to be very large. These large particles take time to vaporize and burn and may therefore, fall to the bottom of the combustion chamber without burning. When the combustion chamber is cold, these large particles form a puddle in the bottom of the combustion chamber. When the combustion chamber is heated, these large droplets or, in some cases, puddles of fuel, eventually vaporize and burn.
There will be more or less puddling or spattering of large particles on the walls of the combustion chamber, depending upon the particular combustion chamber design and the temperature within the firebox. As a result, the combustion chamber or firebox, in a normal home furnace, acts as an afterburner to burn large particles of fuel because the atomization system in a conventional gun burner cannot by itself adequately atomize the fuel.
An oil burner may be 2-3 times larger than is necessary to provide adequate space heating when it is intended that the same burner shall be used to provide hot water in addition to space heating. When outside temperatures are low and hot water demands are high, the burner must be able to satisfy both of these requirements when the demands are at a peak. However, when the demand for heat is low, as in the spring and fall months, and hot water demands are at a minimum, as would be the case at night, the burner still operates at the same firing rate as it does when heating and hot water demands are high. The only difference is that when the requirements are low, the burner may only stay on for quite short period. This is an inefficient mode of operation since, under these conditions the burner cycles on and off many times so that fuel economy is very low. During this short on cycle with such a burner, the burner cannot achieve smokeless operation, and reasonable efficiency, before the thermostat cuts it off. During "off" cycle, much of the residual heat in the furnace is dissipated to the atmosphere and contributes to increased fuel costs.
An innovative approach to fuel burners is illustrated in U.S. Pat. No. 3,425,058, issued Jan. 28, 1969, to Robert S. Babington. The burner therein disclosed represents an adaptation of the liquid atomization principles disclosed in U.S. Pat. Nos. 3,421,699 and 3,421,692 issued Jan. 14, 1969, to the same named inventor and his co-inventors in developing the apparatus and method shown in these patents.
In brief, the principle involved in the aforementioned patents is that of causing a liquid to be atomized to flow over a surface in a highly stressed state, either due to surface tension or due to the particular configuration given to the surface upon which the liquid is discharged.
The surface upon which the liquid is flowed is generally the outside of a plenum chamber having one or more very small apertures over which the liquid flows in a continuous film. Air is introduced into the plenum and passes through the aperture and thereby causes a phenomena in the film whereby very fine micro-sized particles of the liquid are caused to separate from the film in substantial numbers.
By such variations as increasing the number of apertures, the configuration given the apertures, the characteristics of the surface, the regulation of the liquid flow, and/or the regulation of the air pressure, it has been found that not only can great numbers of micro-sized particles be generated but they can be generated in such density that it is impossible to penetrate the resulting spray with light.
It is this basic principle, described above, that was utilized in the development of the very burner disclosed in said U.S. Pat. No. 3,425,058.
In the above-mentioned patent, the developmental burner comprised of simply a cylindrical chamber having a cover thereover, the cover being provided with an aperture adapted to discharge spray generally vertically from the chamber. Disposed within the chamber is a spherical plenum having a lower cone-shaped appendage, the chamber being in communication with a source of air. Liquid is introduced into the chamber so as to flow over the surface of the sphere and drain downwardly along the appendage to a funnel disposed beneath the appendage. The fluid not expended in the combustion process is then discharged back to a sump for recirculation into the liquid system. The plenum is provided with a small aperture centrally located beneath the opening in the cover and the air exiting therefrom creates a fine mist which is discharged upwardly and out of the container for mingling with the atmosphere and combustion occurs at that point.
Means comprising a series of regulatable apertures are also provided in the container below the sphere such that aspirated air can be drawn into the chamber and mingled with the spray as it discharges from the top opening.
From this very simple version of a fuel burner was derived more sophisticated equipment, such as that shown and discussed in an article in the January 1976 issue of Popular Science; entitled "Clog-Proof Super Spray Oil Burner". As noted in the article, one development that evolved was the use of two atomizing heads arranged to discharge the atomized liquids toward one another to create a very high concentration of atomized liquid at a fixed point at which is disposed an ignitor to initiate the combustion process.
A similar arrangement of opposed spray heads is also suggested in U.S. Pat. No. 3,864,326, dated Feb. 2, 1975.
All of the above noted developmental work based on the utilization of the "Babington" principle proved conclusively that the system was perfectly capable of use in a fuel burning system and that, if properly designed, such a system has the potential of evolving into a commercial, practical, highly efficient fuel burner which can be used for domestic heating furnaces. This invention, then, deals with a novel fuel burner, particularly adapted for use in practically every type of domestic heating furnace and in particular, as a retrofit burner for existing heating systems. Grade or fuel oil can be burned with 95% efficiency and at a zero smoke factor within thirty seconds or less from the time of ignition.